1. Field
The present disclosure relates to an electromagnetic damper that inputs an external vibration to an output shaft of an electric motor and generates a damping force with respect to the external vibration by using the electric motor.
2. Description of the Related Art
In Japanese Unexamined Patent Application Publication No. 2006-057668, the purpose thereof is to improve ride comfort of a vehicle, even with a shock absorber that generates a damping force by utilizing an electromagnetic force of a motor (paragraph [0007], abstract). A shock absorber D of Japanese Unexamined Patent Application Publication No. 2006-057668 is provided with a motion conversion mechanism T for converting linear relative motion between a vehicle body B and an axle into rotary motion and a motor M to which rotary motion converted by the motion conversion mechanism T is transmitted. In the shock absorber D, the motor M is fixed to a vehicle body B side, the motion conversion mechanism T is interposed between the vehicle body B and the axle, a sprung side connection mass is reduced, and a force for transmitting input of a vibration from an axle side to the vehicle body B side is reduced. In doing so, ride comfort of the vehicle is improved (Abstract).
The motor M is connected to a control device (not shown) and an external power source (not shown) in such a manner that the motor M is capable of controlling rotary torque of a rotor 1, and the motor M is adjusted so as to obtain a desired damping force. Furthermore, by actively driving the motor M, the shock absorber D is made to function not only as a shock absorber but also as an actuator (paragraph [0016]).
In the shock absorber D (electromagnetic damper) of Japanese Unexamined Patent Application Publication No. 2006-057668, an inertia force (or an inertia moment) is generated when the motion conversion mechanism T converts linear relative motion between the vehicle body B and the axle into rotary motion and when the rotor 1 of the motor M generates rotary torque. With such a configuration in which the inertia force is relatively large, if acceleration of input (for example, input from a road surface) to the shock absorber D is large, the inertia force suppresses changes in stroke of the shock absorber D. Consequently, the vibration damping function of the shock absorber D may not be fully exhibited (for example, in a case where the shock absorber D is used in a suspension device of a vehicle, ride comfort of the vehicle may be reduced).